Let me just nitpick/correct you and mention that Public Domain is not the same
as Free Software or Open Source. The mentioned VirtalBox software is not
public domain but is Free Software.

Free Software and Open Source are copyrigthed software that are explictily
licensed to be open/free. Public domain is software that has no copyright at
all and which according to some aren't even license compatible with lots of
free/open source licenses...